Commentary Aristotle Physics
Book 8. Nature of the First Motion and First Mover
Lecture 1. Whether or not motion began or will end
It remains to consider the following question. Was there ever a becoming of motion before which it had no being, and is it corruption again so as to leave nothing in motion?
Or are we to say that it never had any becoming and is not corruption, but always was and always will be? Is it in fact an immortal, never-failing property of things that are, a sort of life, as it were, to all naturally constituted things?
Now, the existence of motion is asserted by all who have anything to say about nature, because they all concern themselves with the construction of the world and study the question of generation and corruption, which processes could not come about without the existence of motion.
But those who say that there is an infinite number of worlds, some of which are in process of generation while others are in process of corruption, assert that there is always motion (for these processes of generation and corruption of the worlds necessarily involve motion).
But those who hold that there is only one world, whether everlasting or not, make corresponding assumptions in regard to motion.
If, then, it is possible that, at any time, nothing should be in motion, this must come about in one of two ways: either in the manner described by Anaxagoras, who says that all things were together and at rest for an infinite period of time, and that then mind introduced motion and separated them; or in the manner described by Empedocles, according to whom the universe is alternately in motion and at rest—in motion, when love is making the one out of many or strife is making many out of one, and at rest in the intermediate periods of time.
His account is as follows: since one hath learned to spring from manifold, and again one commingled makes manifold arise, thus do things come to be, nor is their era one, nor are they made perfect all at once, and thus they change, but since their motion must alternate be, thus are they always immobile. We must suppose that he means by this that they alternate from the one motion to the other.
We must consider, then, how this matter stands, for the discovery of the truth about it is of importance, not only for the study of nature but also for the investigation of the first principle.
965. After showing in the preceding book that it is necessary to posit a first mobile, and a first motion, and a first mover, the Philosopher intends in this present book to inquire after a description of the first mover, and first motion, and first mobile.
The book is divided into two parts.
In the first, he sets out something necessary to the following investigation: motion is sempiternal.
In the second part, he proceeds to investigate what is proposed, at our enquiry will resolve (253a22; [1004]).
About the first, he does three things: first, he raises a problem; second, he states the truth according to his own opinion, at “let us take our start” (251a8; [971]); third, he answers possible objections to the contrary, at “the arguments that may” (252b7; [997]).
In regard to the first, he does three things: first, he proposes his problem; second, he gives opinions for both sides, at “but those who say” (250b18; [968]); third, he shows the usefulness of this consideration, at “we must consider, then” (251a5; [970]).
About the first, he does two things: first, he proposes the problem he intends to investigate; second, he responds to a tacit question, at “now, the existence of” (250b15; [967]).
966. In regard to the first, it should be known that Averroes says that Aristotle does not intend in this book to inquire whether motion is sempiternal universally, but limits his question to the first motion.
But, if one considers both the words and the procedure of the Philosopher, this is entirely false. For the words of the Philosopher speak of motion in a universal sense. He says in effect: was there ever a becoming of motion before which it had no being and is it perishing again so as to leave nothing in motion? From this, it is clear that he is not inquiring about one definite motion, but about motion universally, asking whether at any time there was no motion.
The falseness of Averroes’ statement appears also from the very procedure of Aristotle.
First, it is Aristotle’s custom always to argue to his proposition from proper causes. Now, if anyone will consider the arguments he adduces, he will see that in none of them does Aristotle argue from a middle term that refers properly to the first motion, but he argues rather from a middle term that is proper to motion in general. Hence, this alone shows that he intends to inquire here about the sempiternity of motion in general.
Second, if he had already proved that there is one or a number of sempiternal motions, he would have been foolish to ask below whether anything is always in motion, for that question would have been already answered. It also is ridiculous to say that Aristotle would return to the beginning of his consideration, as though he had left something out, as the Commentator pretends.
For Aristotle had the opportunity to correct his book and fill in at the proper place any section he had omitted, so as not to proceed in a disorderly way. Now, if this chapter had been treated in the way charged by the Commentator, everything that follows would be confused and disorderly. Nor is this strange, for having supposed an initial impossibility, others then follow.
Furthermore, the correctness of our view is shown by the fact that Aristotle later on uses what he proves here as a principle to prove the eternity of the first motion. He would never have done this had he already proved that the first motion is eternal.
The reason that moved Averroes is wholly frivolous. For he says that, if Aristotle is here intending to inquire into the eternity of motion in common, it will follow that the consideration of Aristotle has been diminished, because it is not evident from what he proves in this place how motions could be always continued to one another.
But this has no weight, because it is enough for Aristotle to prove in this chapter in a general way that motion has always been. But how the eternity of motion is continued—whether it is because all things are always in motion, or because all things are sometimes in motion and sometimes at rest, or because some things are always in motion and others sometimes in motion and sometimes at rest—is a question he raises immediately after the present one.
Thus, the present chapter must be explained according to this intention, namely, that he intends to inquire about motion in common. According to this, therefore, he asks whether motion in common begins to be at some time, such that there will have never previously been any motion, and such that it will perish at some time so as to leave nothing in motion, or on the other hand, whether it never begins and will never cease, such that it always was and always will be.
And he gives an example taken from animals, for some philosophers have said that the world is a certain large animal. For we see animals as alive so long as motion is apparent in them, but when all motion ceases in them they are said to be dead. Accordingly, motion in the whole universe of natural bodies is taken as a kind of life. If, therefore, motion always was and always will be, then this sort of life of natural bodies will be immortal and never-failing.
967. Then, at “now, the existence of” (250b15), he answers a tacit question. For in the preceding books, Aristotle had discussed motion in common, without applying it to things; but now, inquiring whether motion has always existed, he applies his general doctrine about motion to the existence it has in things. Therefore, someone could say that, in this consideration, the first question should have been about whether motion has existence in things, rather than whether it is eternal, especially since there are some who have denied that motion exists.
To this, he responds that all who have spoken about the nature of things admit that motion exists. This is evident from their statements that the world was made, and from their consideration of the generation and ceasing to be of things, which cannot occur without motion. It is therefore a common supposition in natural science that motion has existence in things. Hence, there is no need to raise this question in natural science any more than in other sciences are raised questions about the suppositions of the science.
968. Then, at “but those who say” (250b18), he presents opinions for both sides of the question he proposed.
First, he gives the opinions that declare that motion is eternal;
second, those who declare that motion is not eternal, at “but those who hold” (250b21; [969]).
In explanation of the first part (250b18), therefore, it should be known that Democritus supposed that the first principles of things are bodies that are per se indivisible and always mobile and that the world came to be by the chance aggregation of these bodies—not only the world in which we exist, but an infinitude of other worlds, since these bodies congregated to form worlds in diverse parts of infinite void. Still, he did not posit these worlds as fated to endure forever; rather, some came into existence as a result of atoms combining, and others passed out of existence as a result of the same atoms scattering. Therefore, all the philosophers who agree with Democritus assert the eternity of motion, because they say that the generation and ceasing to be of certain worlds is always going on—and that necessarily involves motion.
969. Then, at “but those who hold” (250b21), he gives the opinions of the other side. And he says that whoever declares that there is just one world that is not eternal also declares what reasonably follows with respect to motion, namely, that it is not eternal.
Therefore, if there be supposed a time in which nothing was in motion, this could happen in two ways, just as it is in two ways that this world could be supposed not always to have been: in one way, that this world began in such a way that previously it never existed at all, as Anaxagoras held; in another way, that the world so began to be that it did not exist for some time previously, but that it again had existed before that time, as Empedocles held.
In like manner, with respect to motion, Anaxagoras said that, at one time, all things were a mixture of one thing with another and nothing was separated from anything else—in which mixture it was necessary to posit that all things were at rest, for motion does not occur without separation, since whatever is in motion separates from one terminus in order to tend to another.
Therefore, Anaxagoras posited the preexistence of this mixture and rest in infinite time, in such a way that at no time before had there been any motion at all, and that it was Mind, which alone was unmixed, that caused motion in the first instance and began to separate things one from another.
Empedocles, on the other hand, said that in one period of time some things are in motion, and again in another period all things are at rest. For he posited love and strife as the first movers of things: love’s property was to make a unity of all things, and strife’s to make many things from the one. But the existence of a mixed body requires a mingling of the elements so as to form one thing, while the existence of a world required that the elements be dispersed in orderly fashion, each to its respective place. Therefore, love is the cause of the coming to be of mixed bodies, and strife the cause of their ceasing to be. But on the contrary, love was the cause of the whole world’s ceasing to be and strife the cause of its coming to be.
Accordingly, he posited that the whole world is being moved when either love makes one from the many or when strife makes many of the one; but during the intermediate times, he supposed there was rest—not in the sense that there was no motion at all, but none with respect to the general change of the world.
Because Aristotle had mentioned the opinion of Empedocles, he also gave the very words, which are difficult to interpret because they are in meter.
Thus, therefore, did Empedocles express his opinion in this arrangement of words: since one hath learned to spring, that is, it is customary for something to be generated, from manifold; and again, that is, in another way, one commingled, that is, composed of a mixture, makes manifold arise, that is, the many come to be through separation—for some things are generated by combining with others, and others by separating.
And according to what we observe in regard to particular instances of coming to be, so thus do things come to be, that is, the same must be understood in the universal coming to be of things with respect to the whole world. Nor is their era one, that is, there is not just one period of duration of things, but at one time a world is generated, at another it is destroyed, and in between there is rest; for “era” is taken to mean the measure of the duration of a thing.
He expresses the distinction of these eras when he adds, thus they change, that is, as though stating that the time in which things pass through the cycle of combining or separating is called one era. And, lest anyone suppose that the generation of a world does not require an era, that is, a period of time, but that the universe comes to be in an instant, Empedocles adds, nor are they made perfect all at once, but after a long interval of time.
Then, speaking of the other era, he adds, thus are they always immobile; that is, in the time between the generation and corruption cycle, he supposed that things are at rest. And, lest anyone believe that there was always change before, and that later there will be continual rest, he excludes this by saying alternate, as though saying that this happens in cycles, namely, that things change and then rest and then change again, and so on to infinity.
Then the words of Aristotle are added to explain the foregoing words of Empedocles, especially the expression thus they change. He says therefore that following the words, thus they change, must be understood the addition, from then hence, that is, from a definite beginning up to the present—not in the sense that motion always was or that, after it began, it had been interrupted.
970. Then, at “we must consider, then” (251a5), he shows the usefulness of considering the question he has proposed. And he says that we must consider just what is the truth about this question, for to know the truth about it is of importance not only for natural science, but the science of the first principle as well, since, both here in book 8 and in the Metaphysics, he uses the eternity of motion to prove the first principle.
This method of proving the existence of a first principle is most efficacious and irresistible. For if, on the supposition that both motion and the world existed forever, it is necessary to posit one first principle, then, if the eternity of it should be rejected, it is all the more necessary, for it is clear that every new thing requires a principle bringing it into being.
Thus the only reason that it could seem that no first principle would be necessary would be if things were from eternity. But, if the existence of a first principle follows even on that supposition—that is, that the world existed from eternity—it is clear that the existence of a first principle is absolutely necessary.